Recently, there is a hot drama "The Legend of Chu Qiao", starring Zhao Liying, Lin Gengxin, Dou Xiao, Li Qin and other appearances, with the blessings of blood, inspiration, abstinence, high appearance, and positive energy. Since the start of the show, it has caused a frenzied discussion among netizens. On July 4, "Chu Qiao Biography" ushered in a historic moment after its launch - becoming the fastest weekly broadcast drama in history to break through the 20 billion online broadcast mark. This is also inseparable from the support of multiple video platforms such as Youku, iQiyi, and Tencent Video.
At the same time that Internet dramas and dramas are blooming everywhere and IP collectives explode, various TV dramas have cooperated with online video platforms to launch synchronous online broadcasts. Today, it is no longer uncommon for TV dramas to have more than 10 billion online broadcasts. The major video platforms have become one of the most important ways of entertainment and daily pastime for netizens because they can provide a large number of types of video content and diversified services. Dare to ask who of us doesn't have a video app on their phone?
Demand also drives technological development. Major online video platforms each use their own trump card, try innovative gameplay, compete for content copyright, and seize users' time and attention. This is a very fierce battlefield without the smoke of gunpowder.
For a long time, Youku Tudou has maintained a market-leading position in the online content and self-made dramas of the video platform. After being escorted by Ali, it is even more prosperous in the field of entertainment. What kind of spark can Alibaba Cloud, another important BU under Alibaba, create with Youku?
In fact, as early as March of this year, Alibaba Cloud announced the merger of Youku CDN, a substantial price reduction of 35%. Although this move has attracted industry manufacturers to follow suit or sigh, it has lowered the threshold for entry into the video industry and provided a rich fertile ground for the entire ecological development.
In terms of video services, there is a saying that the key to good service is transcoding. Alibaba Cloud Video Cloud ApsaraVideo has the industry's unique video transcoding technology - Narrowband HD. Narrowband HD represents a video service concept that reconciles cost and experience. In terms of experience, viewers will be affected by the source definition, resolution, bit rate, frame rate, encoding algorithm, playback strategy, etc. when watching videos. The so-called narrow-band high-definition also hopes to improve the viewer's viewing experience from these perspectives; in terms of cost, the impact Cost factors include bit rate, distribution strategy and playback strategy. Narrowband HD also reduces costs from these three levels.
So how does Alibaba Cloud achieve high-definition in narrowband?
Let's first look at what Narrowband HD does before encoding.
上图是一个视频播放流程图，其中包括了采集、上传、片源修复、转码、编码切片、加密、存储、分发、播放这几步。窄带高清在编码前，基于智能算法来判断视频场景，分析每个视频内容中的场景、动作、内容、纹理等元素，判断视频的类型，根据用户对此类片源的清晰度的预期来设置码率，再根据预设码率选择最佳分辨率。打个比方，如果是好莱坞大片，尽管分辨率只有1536x864，但码率需要设置比较高（3600Kbps）；如果是卡通类内容，尽管分辨率是1920x1080，码率设置依旧会比较低（400Kbps）。
那实现窄带高清的核心原理是什么。
窄带节省不必要的bits，高清是把bits分配到最能产生价值的地方，从而实现，在同样的带宽条件下收看更加清晰的画质。
展开来讲，阿里云转码会把视频内容在直播过程中实时进行分析，通过前置窗口中实时探测视频内容，再设置最合适的码率，同时确保所设置的码率不超出预设值。窄带做到高清的另一个秘诀是根据预设码率选择最佳分辨率，当画面内容特别复杂时，在2Mbps的码率下降低分辨率（720p->480p）；当画面内容较为简单时，可以相应地提高分辨率（720p->1080p）。
经测试，使用阿里云窄带高清，可以用1.2Mbps的平均码率达到1.5Mbps相当的效果，如下图所示
还有一招儿叫画质重生
阿里云窄带高清片源画质重生服务主要提供了四大功能，分别是：
1. 影片标清转高清，常用于传统广电视频处理；传统广电视频采用的编码格式是Deinterlace，阿里云转码器会自动监测是否是该类型的片源，然后进行相应的图像处理，如上图右部分比左部分少了很多毛刺。
2. 2K转4K；分辨率和帧率的提高都会改善用户的观看体验，通过噪声抑制、超分辨率、HDR等技术，将标清画质的经典影片重制为高清版本。
3. 30帧转60帧；利用 Frame Rate Conversion (FRC)技术将主流拍摄设备生成的30帧/秒视频转换为60帧/秒，消除在播放 中的顿挫感。
4. 受损片源修复；对已经受损的片源进行修复，去除过度压缩和介质老化带来的画质损伤，还原低质量片源的用户观感。
在成本方面，传统解码需要18M带宽的视频，阿里云窄带高清可以实现在没有画质损失的前提下仅需要10M带宽，在网络上传输的时候，就相当于给节省了39%的带宽费用，性价比在行业内相当具有竞争优势。
既然这项技术现在已经在优酷上得到了应用，《择天记》和《楚乔传》就是使用了窄带高清，那我们更直观一点，来看下用户侧的感受。下图是腾讯视频、爱奇艺和优酷三家APP在iPhone6S手机上的截屏，三个视频设置都是超清720p，可以十分清楚的看出，优酷的画面质量比另两家要更细腻和优质。
（本截图只做对比使用，版权归版权方所有）
除了转码之外，视频服务的好坏也和网络资源和主机资源直接成正比，阿里云CDN网络以遍布全球的1000多个节点，覆盖六大洲60多个国家和地区的优势，帮助您将视频内容就近传输到用户，实现首屏秒开。除此之外，刚刚正式上线的PCDN拥有遍布95%以上区域和各大运营商的200万个PCDN节点，不仅可以解决大型赛事演出直播、游戏互动直播等场景引发的延时、卡顿等问题，更可以节省四分之三的传统CDN成本。
未来，随着VR在视频领域发挥更多想象，视频的多元化、场景化、临场感将会更加淋漓尽致的体现，在线视频平台的发展皆不可限量。阿里云坐拥最强大的云计算实力和创新能力，据说窄带高清2.0版本即将上线，它又会带给我们什么样的惊喜呢？
原文链接：http://click.aliyun.com/m/25527/